Residents of Mexico City will experience the “Día sin Sombra” phenomenon in May 2026 [1], during which vertical objects cast little or no shadow.
This astronomical event occurs when the sun reaches its zenith, the highest point in the sky. It serves as a visible marker of the Earth's axial tilt and the specific geography of locations within the tropics.
The phenomenon happens because the sun is positioned directly overhead at solar noon [3]. This alignment eliminates the angle required to cast a shadow on the ground for any object standing perfectly vertical. While the event is expected in Mexico City this month [1], similar occurrences have been observed in other regions of the country.
In the Yucatán Peninsula, observers have noted the sun at zenith on July 19-20 [2]. The timing of the event varies by latitude, meaning different cities in Mexico experience the shadowless noon on different dates throughout the year.
Astronomical observers said that this is a natural result of the Earth's orbit around the sun. As the sun's apparent path shifts north and south throughout the seasons, it passes directly over the zenith for various locations between the Tropic of Cancer and the Tropic of Capricorn [3].
For those in Mexico City, the event provides a rare opportunity to witness a precise geometric alignment. The absence of shadows at noon marks the moment the sun is exactly 90 degrees above the horizon [3].
“Vertical objects cast little or no shadow at solar noon.”
The 'Día sin Sombra' is a predictable astronomical event that occurs only in the tropics. Its occurrence in Mexico City highlights the city's position relative to the solar path, serving as a practical demonstration of celestial mechanics and the Earth's tilt.
